The saying "once in a blue moon" refers to something that's exceedingly rare. But you'll have two chances to see this lunar occurrence tomorrow, when a so-called blue moon comes into view.
The first opportunity will be in the morning -- yes, the morning -- as the blue moon is setting for the day, said Anthony Cook, astronomical observer at Griffith Observatory. Look for the early-morning blue moon between 6:30 and 7 a.m., he said.
Later in the day, you'll get a second chance to see the blue moon, when it rises at 7:13 p.m.
So what is a blue moon? It's the second full moon within one calendar month.
The moon isn't actually blue. And it might even take on an orange hue as it starts to rise in the sky, Cook said. If anything, the Friday night moon will most likely appear an especially brilliant white.
"There's nothing unusual really about the moon itself," Cook said. "It will look like the usual moon."
The genesis of the term "blue moon" is unclear.
"It's not really certain" where it came from, Cook said. "Why 'blue' was chosen isn't really known for sure."
There are, on some occasions, atmospheric conditions that could produce a blue-looking moon, he said. And it's believed that such conditions sometimes took place at the same time as the second full moon, perhaps leading to the moniker.